We propose the continuation of pretherapeutic investigations with accelerated high energy (up to 1 BeV/nucleon) carbon, neon, and argon beams at the Berkely Bevalac facility with the aim of understanding the basic biological action of these beams and to furnish a quantitative basis for cancer therapy trials. The program has four parts. Cellular Radiobiology: Studies of the kinetics of survival and of the oxygen effect in synchronized human cell populations in vitro; studies of the sublethal and potentially lethal lesions produced by heavy ions in split and mixed beams; and studies of the nature of molecular lesion in DNA and their repair. Tissue Radiobiology: Acute and chronic responses of normal mammalian organ systems of gut, testes, bone marrow, lung, skin, spinal cord, and brain following single and protracted exposure schedules; and late effects of heavy-ion radiations, particularly harderian gland carcinogenesis. Tumor Radiobiology: The radiobiology of cell spheroids and of rat rhabdomyosarcoma tumors in vivo and in vitro. Radiological Physics and Measurement: Of heavy-ion dose distributions with a new multiwire instrument, MEDUSA, the physics of nuclear fragmentation; the automated control of particle residual range of the beams in tissue using radioactive beams and the design of range filters for therapy.